A typical acoustic ceiling tile is a non-woven structure including a core manufactured from base fibers, fillers, and binders. The base fibers are usually mineral fiber such as mineral wool, fiberglass or the like. The fillers are commonly perlite, clay, calcium carbonate, or cellulose fibers as may be derived from recycled newsprint. The binder is typically cellulose fibers, starch, latex, or similar materials. Upon drying, the binder forms bonds with the other materials to form a fibrous network that provides structural rigidity to the core. To be used as a typical ceiling tile, the core should be substantially flat and self-supporting in order to be suspended in a typical ceiling tile grid or similar structure.
Acoustical ceiling tile may be manufactured using a water-felting process as described in U.S. Pat. No. 5,558,710, the teachings of this patent being incorporated herein. The water-felting of dilute aqueous dispersions of mineral wool and lightweight aggregate is a commercial process for manufacturing acoustical ceiling tile. In this process, a dispersion of mineral wool, lightweight aggregate, binder and other ingredients as desired or necessary is flowed onto a moving foraminous support wire, such as that of a Fourdrinier or Oliver mat forming machine for dewatering. The dispersion dewaters first by gravity and then vacuum suction means; the wet mat is dried in heated convection drying ovens, and the dried material is cut to the desired dimensions and optionally top coated, such as with paint, to produce acoustical ceiling tiles and panels.
For many years, acoustical ceiling tile has also been made by a wet pulp molded or cast process such as described in U.S. Pat. No. 1,769,519, the teachings of this patent being incorporated by reference. According to the teaching of this patent, a molding composition is prepared comprising granulated mineral wool fibers, fillers, colorants and a binder, in particular a starch gel, for molding or casting the body of the tile. This mixture or composition is placed upon suitable trays which have been covered with paper or a metallic foil and then the composition is screeded to a desired thickness with a screed bar or roller, A decorative surface, such as elongated fissures, may be provided by the screed bar or roller. The trays, filled with the mineral wool pulp or composition, are then placed in an oven to dry or cure the composition. The dried sheets are removed from the trays and may be treated on one or both faces to provide smooth surfaces, to obtain the desired thickness and to prevent warping. The sheets are then cut into tiles of a desired size.
In connection with ceiling tiles formed of fiberglass materials, the non-woven layer may be prepared using air-laid processing as particularly described in U.S. Pat. No. 8,563,449, assigned to the assignee of the present application, the teachings of this patent being incorporated by reference. Glass fibers are typically provided with a short size or length suitable for air-laid processing and are relatively more expensive than mineral wool fibers. As generally understood, mineral wool fibers are distinct from glass fibers and ceramic fibers.
As used herein, “air-laid” refers to any method or manufacturing process in which the individual ingredients are suspended in an air or other gaseous stream and that preferably form a web, mat or batt on a porous wire web or other porous carrier surface. The web formation process includes metered or regulated pneumatic or fluidized flow of the web forming materials onto the carrier web where it may be retained in a batt or nonwoven mat form with vacuum assist from below. To that end, the process may include the steps of: (a) raw material dispersing and blending, (b) metering and feeding the raw materials to a head box, (c) air-laid forming the raw materials by deposit onto a porous web or carrier, (e) heating and cooling (f) optionally calendaring, (g) optionally laminating and (h) finishing the web.
The formation of the fiberglass web includes consolidation as by adhesion or thermal bonding. Adhesion bonding may include the application of a discontinuous phenolic, latex or other suitable adhesive to bind the fibers to one another. Thermal bonding contemplates incorporation of synthetic bonding fibers, e.g., generally bi-component fibers with polyethylene and polypropylene. Thermal bonding may utilize oven heating, calendaring or both. In all cases, the adhesive or bonding has little or no effect on the tile noise reduction coefficient value.
For non-woven structures to be suitable for acoustical ceiling tile applications, they generally satisfy various industry standards and building codes relating to noise reduction. For example, industry standards typically specify the acoustical ceiling tile to have a noise reduction coefficient (NRC) according to ASTM C423 of at least about 0.55.
A detailed method of measuring NRC is outlined in ASTM C423. NRC is represented by a number between 0 and 1.00, which indicates the percentage of absorbed sound. For example, an acoustical panel having an NRC value of 0.60 will absorb 60% and deflect 40% of the sound. Another method to test the sound absorption property is estimated NRC (eNRC), which is measured using a smaller sample size via an impedance tube as detailed in ASTM E1050-98.
U.S. Pat. No. 6,443,256, owned by the assignee of this application, discloses a mineral wool dual layer ceiling tile wherein the base mat or layer has low mineral wool content and the surface layer has high mineral wool content. The base mat is indicated to contain 5-25 weight % mineral wool and the surface layer contains 70-90 weight % mineral wool. Other ingredients in either or both layers are indicated to include dyes, pigments, inorganic fillers, antioxidants, surfactants, water repellents, fire retardants and the like. The tile is made by a water-felting process and is indicated to provide a noise reduction coefficient (NRC) of at least about 0.50.